1. Field of the Invention
The present invention relates to a thin film magnetic head, and more particularly relates to the construction of a pinned layer and a bias magnetic layer.
2. Description of the Related Art
A GMR (Giant Magneto Resistance) element is known as a reproducing element for a thin film magnetic head. Conventionally, a CIP (Current In Plane)-GMR element, in which sense current flows in a direction that is horizontal to film surfaces, has been mainly used. However, an element in which sense current flows in a direction that is perpendicular to the film surfaces has been developed in recent years in order to cope with higher density recording. A TMR (Tunnel Magneto-resistance) element which uses the TMR effect and a CPP (Current Perpendicular to the Plane) element which uses the GMR effect are known as elements of this type. In particular, the CPP element has high potential because it has a lower resistance as compared with the TMR element and because it exhibits a large output even for a narrow track width as compared with the CIP element.
The GMR element and the TMR element are provided with a spin valve (hereinafter referred to as SV) which includes a pinned layer whose magnetization direction is fixed relative to an external magnetic field, a free layer whose magnetization direction is changed according to the external magnetic field, and a first nonmagnetic intermediate layer that is sandwiched by the pinned layer and the free layer. The SV is formed in a column shape. The SV is sandwiched by a pair of shield layers which also serve as electrodes for supplying sense current.
It is necessary that the magnetization direction of the pinned layer is firmly fixed without being affected by an external magnetic field. For this reason, a so-called synthetic pinned layer is generally used. The synthetic pinned layer has an outer pinned layer, an inner pinned layer, and a second nonmagnetic intermediate layer that is made of Ru or Rh and that is sandwiched between the outer pinned layer and the inner pinned layer. The inner pinned layer is in contact with the first nonmagnetic intermediate layer and directly contributes to a change in magneto-resistance. The inner pinned layer is antiferromagnetically coupled with the outer pinned layer via the second nonmagnetic intermediate layer, so that the magnetization direction of the inner pinned layer is fixed. Further, since the magnetization direction of the inner pinned layer and that of the outer pinned layer are anti-parallel to each other, the magnetization of the pinned layer is limited as a whole. Accordingly, by using the element as a read element of the head, it is possible to avoid deviation of a bias point that may occur due to the static magnetic field from the pinned layer.
In the synthetic pinned layer, an antiferromagnetic layer that is in contact with the outer pinned layer is often provided in order to fix the magnetization direction of the outer pinned layer. The antiferromagnetic layer is typically made of IrMn. The antiferromagnetic layer fixes the magnetization direction of the outer pinned layer through exchange-coupling with the outer pinned layer. The magnetization direction of the antiferromagnetic layer, i.e., the direction of magnetization of sub-lattices of the antiferromagnetic layer is fixed by annealing. Specifically, the antiferromagnetic layer is magnetized in the direction in which the magnetic field is applied during annealing. In this specification, “annealing” refers to placing a magnetic layer in a magnetic field at a high temperature in order to fix the magnetization direction of the magnetic layer. Further, in this specification, “magnetizing treatment” refers to placing a magnetic layer in a magnetic field at room temperature in order to fix the magnetization direction of the magnetic layer. When the magnetization direction of the antiferromagnetic layer is fixed by annealing, the magnetization direction of the outer pinned layer is aligned with the magnetization direction of the antiferromagnetic layer, and the magnetization direction of the inner pinned layer is fixed in a direction that is anti-parallel to the magnetization direction of the outer pinned layer.
Magnetic layers are provided on both sides of the SV with regard to the track width direction via insulating films, which are made of oxide films, such as Al2O3. This magnetic layer is referred to as a bias magnetic layer, and applies bias magnetic field to the free layer in order to magnetize the free layer into a single magnetic domain. Magnetizing the free layer into a single magnetic domain is effective for improving the linearity of change in resistance that is caused by a change in the external magnetic field, and at the same time, for limiting Barkhausen noise. The bias magnetic layer is formed of a hard magnetic material, such as CoPt and CoCrPt. The magnetization direction of the bias magnetic layer is fixed in the track width direction through magnetizing treatment, which is performed after the antiferromagnetic layer is annealed. In this specification, “track width direction” refers to a direction that is parallel to the track width direction of a recording medium when a slider that includes the element is positioned opposite to the recording medium.
The antiferromagnetic layer has an important role of fixing the magnetization direction of the pinned layer. However, the antiferromagnetic layer does not contribute to a change in magneto-resistance, and additionally causes parasitic resistance. Further, the large thickness of antiferromagnetic layer increases the distance between the pair of shield layers. This is disadvantageous for realizing high recording density, particularly high linear recording density. There is a need to eliminate the antiferromagnetic layer in order to diminish the distance between the shields to achieve high linear recording density.